Fuse



Patented Mar. 23, 1937 PATENT OFFICE FUSE Nicholas J. Conrad, Winnetka,Ill., assignor to Schweitzer & Conrad, Inc., Chicago,lll., a corporationof Delaware Application May 23, 1931, Serial No. 539,436

37 Claims.

This invention relates to fuses in general and more particularly tomeans for sealing the end of a liquid filled fuse tube and providing avent cap therefor.

In my prior Patent No. 1,743,322 of January 14, 1930 I show a fuse knownas the Schweitzer & Conrad fuse which comprises a glass tubesubstantially filled with an arc quenching liquid such as carbontetrachloride or the like and containing, at its upper end, a fuse wirewhich is maintained under tension by a spring and which controls acircuit extending between contact ferrules at the upper and lower endsof the tube. At the upper ferrule there is provided a vent cap which isadapted to be blown outwardly should the pressure within the tube becomeexcessive upon the blowing of the fuse wire, thereby tending to preventshattering of the glass tube. It is to such fuses that the presentinvention is particularly applicable and it is one of the objects of thepresent invention to provide an improved vent cap and means for securingthe same, so as to effectively prevent contamination or outward creepageof the liquid within the fuse tube and yet to permit blowing of the capwhen the pressure within the tube reaches a predetermined value.

In connection with fuses of the kind here contemplated it is highlydesirable that the vent cap be secured in place without the use ofsolder, venting compounds, or other foreign material. Solder and thesoldering process tends to introduce impurities for which the fuseliquid has a great affinity, resulting in internal contamination whichlowers the dielectric strength of the insulating arc quenching liquidused, and also resulting in corrosion of the internal parts,particularly the fuse wire. Also, it is quite difficult to make asoldered joint entirely leak proof to a highly pene- 0 trating, highlyvolatile liquid such as is here used. These are but a few of theobjections to the use of solder and they are equally applicable to theuse of sealing compounds for sealing the vent cap in place. In thepreviously known methods of sealing the vent caps in place there wasalways great difdculty involved in maintaining a uni= iormity. ofblowout pressure and at the same time maintaining a leak proof seal.

It is an object of the present invention to pro-= vide a vent capconstruction which eliminates the use of solder or other foreignmaterial and which admits of close predetermination and control of theblowout pressure, the arrangement being such that the vent cap will blowat the same pressure even after it has been in service for prolongedperiods of time. A definite blowout pressure means:

(a) Prevention of glass breakage.

(b) Building up of definite internal pressure to assist in arc.extinction by the violent passage of the arc extinguishing liquidthrough the are at the time the cap blows.

(c) On extremely heavy blowing there is a positive and certain ejectionof the metal laden vapor resulting in the prompt dissipation anddeionization thereof.

There is another distinct advantage in providing a venting arrangementwhich does not require the use of solder or other sealing compounds. Aspreviously pointed out, it is difficult to make a soldered seal whichwill not contamihate. the insulating liquid used and which will also notbe penetrated by the same. In this type of fuse it has heretofore notbeen practical to replace the fuse link in the field, it being customaryinstead to ship the parts back to the factory for reassembly after thefuse has once blown. In my present fuse thevent cap comprises a thindia-- phragm which is clamped in place, the clamping action beingpreferably around the entire periphery of the diaphragm to provide amechanical seal between the diaphragm and its adjacent part. A nutthreads onto the ferrule for producing the tight clamping action on thediaphragm. This renders the diaphragm easily removable and replaceableto produce a good seal, thereby permitting field reassembly of the fuseafter the fuse link has blown.

Whereas, in prior fuses of the Schweitzer & Conrad type, the closure hasbeen made by a disc or cap of relatively heavy metal sealed to the upperferrule by a joint of graduated strength, according to the presentinvention the closure is made by a rupturable diaphragm, the body ofwhich is graduated to retain only a certain definite pressure. In otherwords, the prior structure graduated the strength of the joint, butaccording to the present invention, the joint is made as firmly as maybe desired, but it is the diaphragm. itself which is graduated to yieldat the desired pressure.

The present invention provides another important function, i. e.,directional control of the gases upon venting of the fuse to atmosphere.

In prior. fuses employing a disc held to the ferrule by a joint ofpredetermined strength, the release of the disc generally begins at somepoint on the periphery which results in the projection of a stream ofarc gases in a lateral direction through such initial opening. Thelateral projection of arc gases is undesirable because it y be directedin such a directionas to cause an interphase fault or fault to ground.Even if the disc should lift evenly on the top of the ferrule. there isnevertheless the tendency to release the arc gases in a sheet at rightangles to the axis of the ferrule and expanding into a cloud. This isknovm as mushrooming of the discharge of the fuse. The same action tendsto occur in the case of a cap blown ofi the end of the ferrule.

According to one phase of the present inven= tion, the thin rupturablediaphragm tends generally to burst at the center and thereby dischargethe arc gases endwise of the housing. This is highly advantageous forthen a definite direction is secured, and the gases issue as a streamand not as a sheet or cloud. Even if the rupturable diaphragm shouldyield first along the margin where it is clamped, the inner tubularwalls of the ring which secures the diaphragm into place tend to directthe gases endwise of the ferrule instead of transversely thereof. Theresult is a direction of the gases in the region intended for thedischarge and. not uncontrollably toward the mounting or adjacentconductors and the like.

The attainment of the above and further on jects of the presentinvention will be apparent from the following specification taken inconjunction with the accompanying drawings forming a part thereof.

In the drawings:

Figure 1 is a partial sectional view of a well known type of fuse towhich my present invention has been applied;

Figure 2 is an enlarged frentary view of a portionoi the fuse shown inFigure l;

Figure 3 is a fragmentary sectional view of a different, and also wellknown, form of fuse to which my invention has been applied:

Figure 4 is a fragmentary sectional view of a portion of the fuse shownin Figure 3;

Figure 5 is a fragmentary sectional view of the top portion of a.ferrule of a fuse such as is shovm in Figures 1 or 3 and illustrating amodified form of my invention; and

Figures 6 to 16, inclusive, are enlarged frag mentary sectional viewsillustrating difierent forms of my invention.

In Figures 1 and 3 I have illustrated two to of my invention applied tofuses of the type shown in my Patent No. 1,743,322 of January 142, 1930to which reference may be hadfor a more complete description of thosefuses. It is, however,

\ to be understood that mypresent invention is not limited to fuses ofthis particular construction,

but that the fuses of this particular construc ion have been shown onlyfor illustrative purposes.

The body of the fuse illustrated in Figure l. is formed of a tube orsleeve i of glass or other suit-= able insulating material upon the endsof which are secured metal ferrules 2 and 3 whichform terminals for theconducting parts of the fuse wire or link contained within the same. Theferrules are secured in position by suitable means providing a seal andpacking for producing a fluid tight joint.

A terminal supporting member it which may comprise merely a fiat springof a generally 8= v shaped formation rests upon a. shoulder on theaccuses and in turn supports a lower terminal member l by means of astrain wire 3 of nichroxne or othehigh resistant material having arelatively grea tensile strength. A fuse wire it serves to main tain theelectrical connections between the terminals it and l. The fuse wire andthe strain wire are both located in a passage i i' formed in a nonconducung plug 5 2 of cork or the like and secured to the upper terminal6 as by making a close fit therewith. A coiled spring is is mechanicallyconnected to the lower terminal 1 and exerts a continuous pull upon thesame to snap it away from the upper terminal when the fuse and thestrain wire yield. A flexible conductor it connects the lower terminal iwith the lower ferrule thereby completing the electrical connectionsbetween the upper and the lower ferrule.

Ween the fuse wire it blows there is a momentary flow of a large currentthrough the high resistance wire 3 which immediately heats and breaksunder the combined action of the heat and the pull of the spring it. Thelower terminot i is thereupon rapidly pulled downward to lengthen thegap between it and the upper terminal. The tube 5 is filled with asuitable insulatlog are quenching liquid such as carbon tetrachloride orthe like for quickly extinguishing any are that may form. A liquiddirector E? is secured to the lower terminal l and moves therewith. Asthe liquid director moves downwardly it violently projects theinsulating liquid into the region of the arc to quickly extinguish thesame.

The portion of the fuse thus far described is well Known in the art anddoes not, per se, constitute the present invention, except incombinatlcn with the parts to be hereinafter described. The fuses ofthis general type must be closed against the entrance of foreignmaterial therein and the closure should be so arranged as to permit anescape of some of the vapors produced upon violent blowing of the fusein the event that the pressure within the tube 8 becomes excessive. ifthis means of escape is not provided then, under such circumstances. theglass tube i will shatter with the consequent objectionable. results.Such fuses are provided with vent caps and the present invention isparticularly concerned with the provision of an improved vent cap and animproved way in which the vent cap is secured in position.

The vent cap comprises an exceedingly thin diap an it which is clampedin place in a cylindrical groove tiformed in the ferrule 2, by means ofan annealed brass ring 22 which is pressed into the groove and thenupset by means of a suitable punch or the like, thereby expanding thesame to produce a very tight clamping action to prevent the creepage ofliquid from within the copper foil of a thickness in the order of .0015inch, although it is to he understood that I am not limited, to thisprecise thickness. The thickness of the foil used is determined by thesize of the opening at the top of the ferrule and the blow-out pressureat which it is desired to have the cap 2% yield. An inverted cup-shapedcap 26 is pressed into the top'of the ferrule 2 in order to protect theexceedingly thin diaphragm 28 against external injury. Any othermeans'for protecting the diaphragm 26 against external injury may used.For instance. as shown in Figure 5, I may use a cap which fits over theoutside of the ferrule 2. It is to be noted that the vent cap it issocured in place without the use of solder or any ing compounds areobjectionable for the reasons previously pointed out. By the presentarrangement I provide a seal which is free of all foreign matter andwhich will blow at a more or less definite pressure which does notappreciably change after the fuse has been in use for a period of time.For renewal of the fuse, the fusible link and its connected terminalscan easily be replaced, The replaceable unit, including the terminals 6and 'I with the terminal head or supporting member 5, is attached to theupper end of the spring, as by means of the screw shown in Figure 1. Thesupporting member 5 slides into place name upper ferrule 2, which has aseat for the same. This supporting member 5 is held in good conductiverelation by the spring as well as by its own contact with the seat inthe ferrule.

In Figure 3 I have shown a fragmentary portion of a somewhat differentform of liquid filled fuse to which my invention has been applied. Inthis form of fuse the upper ferrule 30, which is of a somewhat differentconstruction than that of the ferrule 2 of the fuse shown in Figure 1,is secured to the glass tube l in any desired manner so as to maintain aliquid-tight seal. An annular ring 3| rests upon a shoulder within theferrule 30 and supports a non-conducting washer 32 through which extendsthe shank 33 of an arcing terminal lid. The shank of the arcing terminalis supported against downward movement by a strain wire of nichrome orother high resistance wire of great strength. The strain wire 3:? passesthrough the shank 33 and is secured at each end under the heads ofsuitable screws 36 mounted at diametrically opposite points in theflared or tapered surface 3? or" the ferrule 3d. The top or upper end ofthe shank 33 is provided with a removable screw 38 under which a fuselink 38 is secured at approximately its mid-point. The opposite ends ofthe fuse link 39 are mechanically and electrically connected to thetapered surface 31 or the ferrule at points mid-way between the screws36. The fuse link serves to carry the current from the ferrule 30 to theshank 33 of the terminal 3d whereas the strain wire 35 serves to relievethe fuse wire of any mechanical stress incident to the supporting of theterminal 3%.

A liquid director ll is secured to the shank 33 in any preferred manner,as for instance by means of three screws spaced 120 degrees apart. Ablock 4a is secured to the shank 33 of the terminal in any desiredmanner, as by means of a number of set screws, so as to hold the blockagainst longitudinal and rotative movement on the shank. The lower endof the terminal 34, of which the shank 33 comprises a part, iscounterbored to receive a flexible conductor 45 of high electricalconductivity and is thereafter flattened on the conductor to produce agood electrical joint, as indicated at 5. The conductor corresponds tothe conductor is of the fuse shown in Figure 1 and it is secured at itslower end to a ferrule corresponding to the ferrule 3 of the fuse shownin Figure l. A spring i5 is secured to the block 44in any desiredmanner, as by means of a pair of onset projecting pins ill- 3? whichcooperate with the upper convolutions of the spring. One or more of thescrews which secure the block 44 to the terminal 3d may also be utilizedto help secure the upper end of the spring to the block #4. Wire guidingfingers fit are'secured to the terminal 3 5 and guide the terminal 7within the tube 3 as the terminal snaps downward under the action of thespring 46 when the strain wire gives upon blowing of the fuse.

Upon occurrence of an overload the fuse 39 blows thereby removing theshunt across the strain wire 35'between the terminal shank 33 and theferrule 30. The high resistance strain wire therefore immediatelybecomes heated and under the combined action of the heat and the tensionof the spring 46 it gives, thereby releasing the shank 33. The terminal34 is immediatelysnapped downward under the action of the spring toincrease the gap in the circuit between the upper and the lowerterminals. The fuse tube i is filled with insulating arc quenchingliquid substantially to the level of the washer 32 and as the terminal34 recedes the arc is drawn into this insulating liquid. In addition,the liquid director 34 violently projects fresh liquid into the regionof the arc as the liquid director is drawn downward with the terminal.The are is therefore quickly extinguished. It is to be noted that thearc is initially drawn in the region above the washer 32 which regioncomprises an explosion chamber. The upper portion of this explosionchamber is provided with a vent cap which constitutes a releasable wall.In the event of a viclent blowing of the fuse the resulting pressure maybecome excessive, in which case the vent cap is ruptured therebypermitting the escape of the metallic vapors and preventing such a highrise of pressure as would shatter the glass tube l.

The present invention is particularly concerned with the construction ofthe vent cap which has been shown as applied to an otherwise standardand well known form of fuse for illustrative purposes only, it beingunderstood that the venting arrangement, to be presently more fullydescribed, is equally applicable to othertypes of fuses.

The upper portion of the ferrule 35] is internally threaded as indicatedat 5d, the threads terminating at a shoulder 5i which extends around theinside of the ferrule and is provided with an upstanding circular ridge52 having well rounded edges. The vent cap comprises a circular metallicdiaphragm 53 which is exceedingly thin and may comprise hard copper foilof a thickness in the order of .0015 inch, although this thickness maybe departed from to a considerable extent in order to provide the properstrength for the diaphragm to sustain a predetermined maximum internalpressure. A gasket 54 of annealed brassor the like is interposed betweenthe diaphragm 53 and a nut 55 which is threaded into the threads 50 atthe upper end of the ferrule and which securely clamps the diaphragm 53in place. The nut 55 comprises a circular ring open on top to permit theescape, of

the pressure which causes the blowing of the diaphragm 53. The nut 55affords a protection against external injury of the diaphragm 53. The

nut 55 serves a further useful function in preventing injury by the arcto the ferrule. The ferrule is a permanent part of the fuse housing,whereas the nut 55 is replaceable. Sometimes in the blowing of a fuse ofthis type. the arc persists and it will burn and injure the uppermostpart of the ferrule to which the extremity of the arc is driven by theoutward flow of arc extinguishing material. The nut 55 forms anextension of the upper end of the ferrule, and injury to it by the arcis not serious, inasmuch as the nut 55 is replaceable. The same functionis performed by other forms herein disclosed, in which the clamping nutor ring forms an extension of the ferrule. If desired, an additional capmay be fitted over the end of the ferrule 3h toi'urther protect thediaphragm against external injury. The additional cap does not make sucha tight fit as would prevent its expulsion upon blowing of thediaphragm.

An arrangement including an externally fitted cap for further protectingthe diaphragm is illustrated in Figure 5. In this case I haveillustrated only a portion of the upper end of a ferrule which portionmay be representative of the ferrule of the fuse shown in Figure 3 or ofthe ferrule of the fuse shown in Figure l. The diaphragm is indicated athe, the clamping nut at ti, and the protecting cap at 62. The diaphragmmay comprise a somewhat softer disc than the disc 53 of Figure 4-. inwhich case a somewhat thicker material is used with the result that thebrass washer or gasket 5% of Figure 4 may be omitted. It is however tobe understood that the diaphragm as may be made of harder material, inwhich case it is thinner, and a soft ring gasket is used.

In Figures 6 to 16, inclusive, I have illustrated various modificationsof my invention. In these figures only a portion of the upper ferrulehas i been illustrated and while I have shown in connection with some ofthe modifications a ferrule the top of which is provided with a taperedportion corresponding to the portion 3? of Figure 3 and in other of themodifications a ferrule of the type corresponding more nearly to thatshown in Figure 1, it is to be understood that these showings are merelyillustrative and the venting arrangements shown in any of these iiguresmay be applied equally well to either type of ferrule or to ferrulesspecifically different from the ferrules here illustrated. In the formof my invention illustrated in Figure 6, the diaphragm 65 is wedged intoa tapered groove or slot 656 formed in the shoulder El of the ferruleand extending around the entire periphery of the same. A wedge 68comprising an endless ring is jammed into the groove 66 by means of anut as which is threaded into the ferrule. The taper on the wedge ispreferably made very small, in the order l of 5 or degrees, so that thewedge may be forced into place to a considerable extent in order toproduce a tight seal around the entire periphery at idl l. The rim ofthe diaphragm I5 is curved around the lower curved edge of the wedgering is and is wedged in place by means of -a nut 76 which threads intothe ferrule and forces the wedge ring against the corner of a shoulderll extending around the inside of the ferrule. As the nut 16 is turneddownward the lower edge of the wedge ring 13 is extended outwardly toproduce a liquid tight seal around the entire periphery of the diaphragml5. It is to be noted that in this arrangement there is produced ineffect two seals, one along the ring where the wedge 13 jams thediaphragm against the horizontal portion of the shoulder ill and theother along the ring where the wedge It bears against the verticalportion 'on the inside of the ferrule.

In Figure 8 I have shown an arrangement which is very much similar tothat shown in Figure '7, difiering therefrom mainly in that I here use adiaphragm which is upwardly curved. 'I'he curaovasse vatureapproaches'that of a portion of a spherical surface, and the lower edgeof the clamping nut 56 is curved as indicated at iii to conform withthis surface. Since the portion of the diaphragm that bears against thecurved surface Si or" the nut is reinforced at itsback by this clampingnut, it is apparent that the total unpacked area of the diaphragm whichmust oppose the internal pressure resulting from the blowing of the fuseis materially decreased, as a result of which a thinner diaphragm may beused or, stated conversely, a diaphragm of the same thickness may beused upon a fuse ferrule of an appreciably larger internal diameter.

In Figure s I have illustrated an arrangement for clamping the diaphragmin place by the use of an endless ring of a triangular cross section.The endless ring is illustrated at 85 and is held in place by a nut t6provided with a generally curved lower corner 8'? which "nears againstthe triangular wedge 85. In other respects this clamping arrangement issimilar to that shown in Figure 8.

In the arrangement shown in Figure 10, a clamping ring so, of a somewhatdifierent cross section, is used. The lower surface of the clamping ringso is well rounded and presses the diaphragm against a shoulder on theferrule along substantially a circular line. The clamping nut isindicated at 9i and the foil diaphragm at at.

In the form of my invention illustrated in Figure 11 the seal betweenthe diaphragm and the ferrule is formed by clamping an endless wire ringQ5 between the nut 85 and the diaphragm. The lower outer corner of thenut 96 is tapered or chamfered oif so that upon tightening of the nut 95the wire ring 935 is forced outwardly and downwardly, thereby jammingthe diaphragm against the ferrule along the entire periphery of thedia-- phragm.

In the form of my invention illustrated in Figure 12 the diaphragm 9? ismade of a somewhat larger diameter with the outer portion thereof foldedaround the endless circular wire ring 95 and then bent back upon itself.The wire ring 95 with the diaphragm folded around it bears against theshoulder within the ferrule, the corner of which shoulder is preferablyoutwardly and downwardly tapered as indicated at 98. The diaphragm withthe wire ring 95 therein is clamped in place by the clamp nut 95, agasket 99 of an-' healed brass or the like being interposed between thenut and the diaphragm. A

In Figure 13 a filler ring Hill bears against a self-expanding gasketiii! of annealed brass or the like in theform of an endless ring thatbears against a shoulder m2 and the cylindrical wall of the ferrule. Theupper portion of the filler ring ltd is well rounded asindicated at weand it is upon this well rounded ring that the diaphragm ili l rests.Agasket m5 of annealed brass or the like is interposed between thediaphragm ltd and the clamping nut me which threads into the ferrule andclamps the diaphragm against the filler ring and the filler ring againstthe gasket Mi. The gasket mi provides a liquid tight seal for preventingthe outward creepage of the liquid from the fuse along the inner wallsof the ferrule. The diaphragm iiil provides a liquid tight seal at itscontact with the curved portion we of the filler ring Hit. By usingfiller rings of various sizes the size of the vent opening may bevaried.

The form of my invention illustrated in Figure 14 differs from thatillustrated in Figure 13 in two respects. In this form of my inventionthe filler ring, which is indicatedat MD, threads into the ferrule anditself exerts a pressure upon the gasket IOI independently of theclamping nut I06. A second difference between this filler ringterposedbetween the diaphragm- I04 andthe clamping nut I06.

clamping nut I06 acts as a lock nut to lock the In this arrangement thefiller ring in place.

In the form of my invention illustrated in Figure 15 the brass fillerring I I5 is provided with an outwardly projecting circular rim H6 atthe bt-' tom thereof, the outer edges of the rim being well erablycopper, is interposed between the filler I I and the ferrule. The ringI" is preferably of a thickness in the order of .005 inch, although thepresent invention is not limited to this particular size. The top of thefiller ring II! is provided with circular ridges or corrugationsextending around the entire periphery thereof as indicated at I I8. Therolled copper diaphragm vent cap is indicated at I20, said ventcap beingheld in place by means of the nut I2I and the washer I22 as in the formshown in Figure 14. The foil III provides a seal for preventing theoutward creepage of liquid along the inner wall of the ferrule and thediaphragm I20 constitutes a vent cap as previously explained.

In Figure 16 I show still another means for securing the vent cap in.place. In this arrange-, ment the upper inner shoulder on the ferruleis provided with a plurality of circular depressions I21 extendingaround the shoulder and forming corrugations across the top of theshoulder. The washer I28 is provided with similar mating projections.The diaphragm I30 is clamped in place between the shoulder on theferrule and the projections on the washer I28. The nut I20 threads intothe top of the ferrule and exerts its clamping action through the washerI28 to tightly clamp the diaphragm I30 in place to produce a liquidtight seal between it and the ferrule.

In each of the forms of my invention illustrated in Figures 6 to 16,inclusive, I have not illustrated an additional cap, such as the cap 62of Figure 5, for protecting the diaphragm against external injury. It ishowever to be understood that such a cap may be provided for any of theforms of my invention above referred to, if desired.

A thin circular diaphragm held rigidly at: the edges and subjected tointernal pressure tends to burst at the center if its radius ofcurvature begreater than the radius of the opening. This is of distinctutility in the present device in causing the gases to bedischargedendwise, and not later ally. Even if in the forms justreferred to, the diaphragm be weakened at the margin by the clampingpressure, so that the diaphragm should begin to tear first at the edgeof the clamping ring, the internal tubular walls of the clamping ringdirect the gases endwise and avoid the lateral squirting effect or themushrooming effect of the gases caused by blowing off a nonsrupturabledisc sealed by a yieldable seal at the end of the ferrule.

In compliance with the requirements of the patent statutes 1 scribed afew preferred embodiments of my invention. It is however to beunderstood that the invention is not limited to the precise arrangementherein shown, the same being merely illushave herein shown and de-'ratlve of the general principles of the invention.

What I consider new and desire to secure by Letters Patent is:

1. A fuse comprising a tubular member having contact ferrules at theopposite ends thereof and a fuse wire maintaining an electric connectionbetween them, spring means normally under tension and released uponblowing of the fuse to produce an extended gap in the circuit betweenthe ferrules, a bath of insulating arc quenching liquid within thetubular member for quenching any are that may form during the drawing ofsaid gap, and a vent cap closing the top of the upper ferrule andadapted to be blown outwardly upon the violent blowing of the fuse, saidvent cap comprising a diaphragm mechanically clamped along its entireperiphery tightly against the ferrule by curved. An'L-shaped ring III ofthin foil, pref-- means including a nut threaded to the ferrule and awedge held in position by the nut, said clamped diaphragm providing aseal against outward creepage of the liquid within the tube which sealis free of self setting plastic sealing compounds.

fusible conductor, said disc comprising a diaphragm mechanically clampedalong its entire periphery tightly against the ferrule, said clampeddiaphragm providing a seal 'against outward creepage of the liquidwithin the tube which seal is free of self setting plastic sealingcompounds,

and an outer cap member above the disc to protect the disc againstexternal injury, said outer cap being blown away upon violent blowing ofthe disc.

3. A fuse comprising a tubular member having ferrules at both endsthereof and a fuse link maintaining an electrical connection betweenthem, spring means normally under tension and released upon blowing ofthe fuse to produce an extended gap in the circuit between the ferrules,anexplosion chamber and an arc quenching liquid both within the tube forquenching any arc that may form during the drawing of said gap, saidexplosion chamber having a releasable end wall comprising a diaphragmclosing off the same, and means for clamping the end wall in place toform a liquid-tight seal between the end wall and the explosion chamber.

4. A fuse comprising a tubular member having ferrules at both endsthereof and a fuse link maintaining an electrical connection betweenthem, spring means normally under tension and released upon blowing ofthe fuse to produce an extended gap in the circuit between the ferrules,an explosion chamber and an arc quenching liquid both within the tubefor quenching any are that may form during the drawing of said gap, saidexplosion chamber having a releasable end wall comprising a diaphragmsealing off the same, and means for clamping the end wall in place, saidmeans comprising a jam nut having threaded engagement with one of theferrules.

5. A fuse comprising a. tubular member having ferrules at both endsthereof and a fuse link maintaining an electrical connection between.them, spring means normally under tension and wall in place, said meanscomprising a jam nut and a wedge exerting a clamping action along theentire periphery of the releasable endwall. I

6.1 fuse including an open top receptacle containing a liquid arcquenching dielectric, a

, closure for the open top comprising a diaphragm of metal foil, andmeans clampingthe foil in place to provide a liquid tight seal, saidmeans including a wedge contacting with the foil along the entireperiphery'thereof.

7. A. fusev including an open top ferrule at the upper-end thereof,afusible link adjacent said ferrule, a vent cap comprising a thin,fragile diaphragm member sealing the open top of the ferrule, and ascrew threaded member thread d on the top of the ferrule and clampingthe diaphragm in place and sealing the top of the ferrule said linkhaving a terminal connecting it with said ferrule independently of saiddiaphragm. 4 I

8. A fuse including an open top ferruleat the upper end thereof, afusible link adjacent said ferrule, a vent-cap comprising a thinrupturable diaphragm member sealing the open top of the ferrule, ascrewthreaded member threaded on the top of the ferrule and clamping thediaphragm in place and sealing the top of the ferrule, and a second capspaced from and overlying the diaphragm to protect the same from external injury, saidi link havinga terminal connecting it with saidferrule independently of said diaphragm, said terminal being expellablefrom the receptacle when'the diaphragm is ruptured by the internalpressure created upon blowing of the link. I

9. A fuse including an open top ferrule at the upper end thereof, a ventcap comprising a thin diaphragm member sealing the open top of theferrule, said vent cap being mechanically separate and readily separablefrom the ferrule to permitreplacement of the parts within the fusethrough the open topof theferrule, and a removable clamping member onthe fuse external of the diaphragm, said clamping member clamping thediaphragm in place to form a sealfor the open end of the fuse by theclamping action on the diaphragm.

. 10. A fuse including an open top ferrule at the upper end thereof, avent cap comprising a diaphragm' member closing the top of the ferrule,and means for sealing the diaphragm in place comprising a wedge ringaround the entire periphery of the diaphragm wedging the same in place.

11.,A fuse including an open top ferrule at the upper end thereof, avent cap comprising a diaphragm member closing the top of the ferrule,and means for sealing the diaphragm in place comprising a wedge ringaround the entire periphery of thediaphragm wedging the same in place,anda nut jamming the wedging ring in place.

' 12. A fuse including an open. top ferrule at the upper end thereof,said ferrule having a cylindrical groove formed therein between itsinner and its outer ends, a vent cap comprising a diaphragm memberclosing the top of the ferrule, the periphery of the diaphragm extendinginto the groove, and a wedge ring also extending into the groove andtightly wedging the diaphragm member in place to provide a liquid tightseal along its periphery.

13. A fuse including an open top ferrule at the upper end thereof, saidferrule having a cylindrical groove formed therein between its inher andits outer ends, a vent cap comprising a diaphragm member closing the topof the ferrule, the periphery of the diaphragm extending into thegroove, a wedge ring also extending into the groove and tightly wedgingthe diaphragm member in place to provide a liquid tight seal along itsperiphery, and a threaded nut jamming the wedge in place.

l4. A fuse including an open top ferrule at the upper end thereof, saidferrule having a cylindrical groove formed therein between its inner andits outer ends, a vent cap comprising a diaphragm member closing the topof the ferrule, the periphery of the diaphragm extending into thegroove, a wedge ring also extending into the gs: and tightly wedging thediaphragm memberin place to provide a liquid tight seal along itsperiphery, a threaded nut jamming the wedge in place, and an outwardlyexpellable cap member for protecting the vent cap against externalinjury. I

15. A liquid filled fuse including an open top ferrule, a thin metallicdiaphragmclosing the top of said ferrule and means for clamping thediaphragm. in place to provide a liquid tight seal free of foreigncompounds, said means comprising a self-expanding wedge ring, and a nutthreaded onthe ferrule and clamping the wedge Y top of said ferrule andmeans for clamping the,

diaphragm in placeto provide a liquid tight seal free offoreigncompounds, said means comprising a self-expandingwedge ringcomprising an endless wire of a circular cross section, and anutthreaded on the ferrule and clamping the wedge ring along the entireperiphery of the diaphragm.

18. A liquid filled fuse including an open top ferrule, a thin metallicdiaphragm closing the top of said ferrule and means for clamping thediaphragm in place to provide a liquid tight seal free of foreigncompounds, said means comprising a self-expanding wedge ring, and a nutthreaded on the ferrule and clamping the wedge ring along the entireperiphery of the diaphragm, said nut being substantially sphericallyshaped on its inner side against which the diaphragm bears adjacent itsrim.

19. A liquid filled fuse including an open top ferrule, means forpreventing outward creepage of liquid along the inner wall of theferrule, said means comprising a metalliacircular member and a nutthreaded on the ferrule and clamping said member in place along theentire periphery of the member, a vent cap for closing the top of theferrule, and means including said nut for clamping said vent cap inplace.

-20. A liquid filled fuse including an open top ferrule, a fusible linkconnected to said ferrule, a filler ring at the top of the ferrulemaking a liquid tight joint therewith, a thin diaphragm on top of thefiller ring, and a clamping nut threaded on the ferrule and clamping thediaphragm in place to form a liquid tight seal said connection of saidfusible link to said ferrule being independent of the filler ring andthe diaphragm.

21. A liquid filled fuse including an open top ferrule, a filler ring atthe top of the ferrule making a liquid tight joint therewith, a thindiaphragm on top of the filler ring, and a clamping nut threaded on theferrule and clamping the diaphragm in place to form a liquid tight seal,the top surface of the filler ring having circular corrugations and theedges of the diaphragm being clamped into the corrugations.

22. A liquid filled fuse including an open top ferrule, a filler ring atthe top of the ferrule making a liquid tight joint therewith, a thindiaphragm on top of the filler ring, and a clamping nut threaded on theferrule and clamping the diaphragm in place to form a liquid tight seal,the top surface of the filler ring having circular corrugations and theedges of the diaphragm being clamped into the corrugations by meansincluding a gasket having mating corrugations.

23. In a fuse 'of the type comprising a sealed casing having an arcquenching liquid for quenching the arc formed upon blowing of the fuse,means for protecting the casing against the building up of excessivepressures by the vaporization of the arc extinguishing liquid, saidmeans including a rupturable diaphragm closing an opening in the casing,and clamping means sealing the diaphragm to the casing.

24. A sealed fuse comprising a tubular member having a ferrule at itsupper end, a replaceable fusible unit having means at its lower end forsecuring it to a tension spring and contact .means at its upper endcooperating with the inside of the ferrule below the top thereof forsupporting the unit from the ferrule, whereby it is held in place by thepull of the spring, a rupturable diaphragm at theouter end of theferrule and sealing the same, and a member clamping the diaphragm inplace independently of the contact means to form 'a fluid-tight seal bythe clamping pressure.

25. A sealed fuseof the type comprising a tubular member containing afuse link and substantially filled with an arc quenching liquid andhaving a vent, characterized by-the fact that the fuse is made tofacilitate refilling after blowing of the link, said vent cap comprisinga vent cap in the form of a rupturable diaphragm and a threaded clampingmeans clamping the diaphragm in place to form a liquid tight seal byclamping pressure.

26. A sealed fuse of the type comprising a tubular member havingferrules at both ends thereof, means including a fuse link maintaining acircuit between the ferrules, spring means normally under tension andreleased upon blowing of the link to draw a gap in the circuit, an arcquenching liquid for quenching any are that may form during the drawingof the gap, and a vent cap, characterized by the fact' that the fuse ismade to permit refilling, said vent cap being in the form of arupturable diaphragm and means for sealing the diaphragm in placeincluding a clamping nut whereby the fuse may be refilled and rescaledin the field by clamping a new diaphragm in place.

27. A sealed fuse of the type herein disclosed, comprising a tubularhousing enclosing a charge of arc extinguishing material, said housinghaving a ferrule fixed at the upper end thereof, said ferrule having aterminal seat, and a seat for a diaphragm, said seats being independentof each other, a replaceable fuse unit comprising a fusible link, aspring in the housing for separating the terminals of the link uponfusing of the same, said replaceable unit having a separable couplingwith the spring and having a terminal slidable into engagement with theterminal seat, a rupturable diaphragm engaging said diaphragm seat, anda replaceable mechanical clamping member for clamping said diaphragm tosaid seat to form a readily renewable seal, said diaphragm beingrupturable at a predetermined pressure-to permit expulsion of theproducts of the arc and of the arc extinguishing material.

28. A sealed fuse of the type herein disclosed,

comprising a tubular housing enclosing a charge of arc extinguishingmaterial, said housing having a ferrule fixed at the upper end thereof,said ferrule having a terminal seat and a seat for a diaphragm, saidseats being independent of each other, a replaceable fuse unitcomprising a fusible link, a spring in the housing for separating theterminals of the link upon fusing of the same,

said replaceable unit having a separable coupling 3 with the spring andhaving a terminal slidable into engagement with the terminal seat, arupturable diaphragm engaging said diaphragm seat, and a replaceablemechanical clamping member for clamping said diaphragm to said seat toform a readily renewable seal, said diaphragm being rupturable at apredetermined pressure to permit expulsion of the products of the arcand of the arc extinguishing material, said clamping member constitutinga ring which forms an extension of the ferrule, said ring serving tosustain the are formed upon blowing of the fusible link and serving tosave the ferrule from injury by the arc.

29. A sealed fuse of the type comprising a fuse housing employing atubular sleeve of insulation having an upper ferrule sealed thereto, anupper fuse terminal in the housing connected to said ferrule, a fuseconnected to said terminal, and a releasable closure for the ferrulecomprising a thin disc of metal exposing a definite area to internalpressure and being of a thickness and material so calibrated as topermit rupture thereof substantially at a predetermined pressure whichis less than that which wou d injure the remalnder of the housing, and ascrew threaded ring readily attachable for securing the disc over theopening of the ferrule in fluid tight condition,

of substantially at a predetermined pressure which is less than thatwhich would injure the remainder of the housing, and a screw threadedring readily attachable for securing the disc over the opening of theferrule in fluid. tight condition, said disc and its attaching meansbeing spaced from the terminal to remove the disc from the ind ace ofthe fuse terminal'ancl fuse, and a proton 1e device carried on the upperferrule and mechanically shielding the thin disc from external injurywhich would change the calibration and hence the pressure at which itwould rupture.

31. A device of the class described, comprising ahousing adapted tocontain a liquid fill and comprising a sleeve with an open ferrule atits upper end and a closed ferrule at its lower end, a renewable fuselinl: having terminals and being connected between the ferrules, saidlink being readily renewable, a spring for tensioning the link, areadily renewable seal for said upper ferrule, said seal comprising adisc of calibrated thickness and ofa material suitable to provide adefinite rupturing value for internal pressure and threaded means forsecuring the disc to the ferrule to close and seal the housing.

32. A device of the class described, comprising a housing adapted tocontain a liquid fill and comprising a sleeve with an open ferrule atits upper end and a closed ferrule at its lower end, a renewable fuselinlr having terminals and being connected between the ferrules, saidlink being readily renewable, a spring for tensioning' the link, areadily renewable seal for said upper ferrule, said seal comprising adisc of calibrated thickness and of a material suitable to provide adefinite rupturing value for internal pressure, and threaded means forsecuring the disc to the ferrule to close and seal the housing, saidseal being independent of the fuse terminals, and pro tective means forthe seal to guard it against external injury. 1

33. A sealed fuse comprising a tubular member having a ferrule at itsupper curl, a replaceable fusible unlt having means at its lower end forsecuring it to a tension spring and contact means at its upper endcooperating with the inside of the ferrule below the top thereof forsupporting the unit from the ferrule, whereby it is held in place by thepull of the spring, said 6ontact means being readily replaceable uponre-fusing the device, a rupturable diaphragm at the outer end of theferrule and sealing the same, and a readily replaceable member clampingthe diaphragm in place independently of the contact means to form afluid-tight seal by the clamping pressure, said clamping membercomprising a tubular extension above the diaphragm for directing thegaseous products of blowing of the fusible unitendwise of the tubularmember.

34. In a fuse of the class described, a tubular fuse housing having anopen ferrule at one end,

a fusible linl; and cooperating arc extinguishing v material within thehousing, a thin rupturable diaphragm of predetermined strength to resistpressure closing said open ferrule, and means providing a tubular wallextending endwise of the housing beyond the diaphragm and serving todirect the gaseous products of blowing of the fuse arc extinguishingmedium, and having a vent for the end of the fuse characterized by thefact that the fuse is made to facilitate refilling after blowing of thefuse, said vent comprising a closure in the form of a rupturablediaphragm, and a ring clamping the edges of the diaphragm to the ferruleto form a fluid-tight seal by clamping pressure, said ring providing aninner peripheral axially extending wall which tends upon rupture of thediaphragm to direct the gaseous are extinguishing medium and the arcvapors endwlse of the housing.

36. In a fuse, a fuse housing terminating in a tubular open endedferrule, a fusible link in the housing and are extinguishing material inthe housing acted upon by the blowing of the fuse to produce a gaseousmedium, and a diaphragm disposed across the bore of the ferrule belowthe free end thereof, said diaphragm being removable by internalpressure of said gaseous medium at a value less than that which wouldcause failure of the housing, and the end of the ferrule beyond thenormal position of the diaphragm causing the gases when released to beprojected substantially endwise away from the fuse housing.

87. The combination of claim 35, characterized by the provision of arelatively stiff backing plate disposed in reenforcing engagement withthe rupturable diaphragm which is thin and flexible, said backing platehaving holding means by which it is releasably held to the casing with apredetermined resistance to displacement, said thin rupturable diaphragmforming a fluid-tight closure for the casing keeping the backing plateand its holding means normally out of contact with the contents of thehousing but transmitting the internal pressures to said backing platewhereby the internal pressure must rise to a definite value which willovercome the predetermined resistance of the plate to displacementbefore rupture of the diaphragm can occur, the diaphragm alone beingrupturable by internal pressures substantially less than that requiredto dis= place the backing plate.

NICHOLAS J. CONRAD.

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